Television system



June 6, 1944. H. E. KALLMANN TELEVIS ION SYSTEM Filed Aug. 2'7, 1941 2Sheets-Sheet l TIME FREQUENCY- MC 7:)

Y AQ M m .R mEWWm V A 2 w E m Patented June 6, 1944 UNITED STATES"PATENT OFFICE TELEVISION SYSTEM Heinz E. Kallmann, New York, N. Y.,as'signor to Radio Corporation of America, New York, N. Y a corporationof Delaware Application August 27, 1941, Serial No. 408,579

7 Claims.

This invention relates to a, television system and more specifically toa system of television transmission and reception in which only a singlecarrier is used for the trion of both the video signal and theaccompanying audio signal.

The transmission of video and accompanying audio signals in televisionsystems on a single transmitter has been suggested in the past, but allof these so suggested systems have suffered from drawbacks which haverendered them impracticable. for one or another reason. My inventionprovides a television transmitting and receiving system which makes useof onlya single transmitter for transmitting the video and sound signalsand receiving these signals on a single receiver, while overcoming allof the drawbacks of previous systems, and introducing, in addition, anumber of advantages not present in television systems known to theprior art. In accordance with my invention, the carrier of the singletransmitter is amplitudeor frequencymodulated with video signals for apredetermined length of time. Thereafter the carrier is shifted infrequency to provide the line synchronizing impulses. The shiftedcarrier providing line frequency impulses is frequency-modulated by thesound signals. Periodically at the end of each frame the carrier isshifted to a third frequency to provide the frame synchronizingimpulses, The predetermined time of transmission of the video signal hasa time duration equal to transmitting one line of the picture, while thepredetermined time during which the line synchronizing impulse istransmitted is made equal in time duration to that allowed for thereturn line or flyback time. It will be noted that'the sound signals aretransmitted only during the line synchronizing pulses. As is well knownin the prior art, where the line frequency is high and is above themaximum sound frequency sought to be reproduced, highly satisfactorysound reproduction can be obtained; that is to say, that it is notnecessary that the 7 sound transmission be continuous, but may beinterrupted at a relatively high rate without introducing objectionabledistortion, While it is known toltransmit sound intermittently durthisis especially true of subcarrier modulation.

By my invention, where the line synchronizing impulses are wide-bandfrequency-modulated by. the sound, the signal-to-noise ratio becomesvery high.

The advantage accruing from my new, improved and novel system oftransmitting and receiving television images and sound are: (1) only asingle transmitter is required; (2) in a given channel a wider band offrequencies is available for television proper to provide betterdefinition; (3) better signal-to-noise ratio is provided for line andframe synchronizing signals, resulting in better synchronization; (4)improved signal-to-noise ratio is obtained for sound transmission; (5)cross modulation, or

any other interaction, between the sight and sound signals is completelyavoided; (6) cross modulation or interference between the line and framesynchronizing signals is also eliminatel.

By utilizing only a single transmitter, in accordance with my invention,the entire frequency band of a given television channel is availableduring the picture transmission time for picture signals. This resultsfrom the fact that no fre-v quency band needs to be provided for aseparate audio carrier with intervening guard bands between this carrierand the maximum frequency of the video channel, so that efiectivelysubstantially another megacycle of band width is added to the videochannel.

By shifting the carrier to a new frequency to provide the linesynchronizing signal and shifting the carrier to yet another frequencyto provide the frame synchronizing signal, and providing these shifts atdifferent times, better signal-tonoise ratio is obtained, since bothamplitude and frequency selection can be utilized for the synchronizingsignals. As is well known, the noise is a function of the band width, sothat if at the receiver the band width for the synchronizing signals iseffectively reduced, the noise is correspondinglyreducedwhichautomatlcally'improves different time intervals and on different shiftedingthe return line time in television systems,

the signal-to-noise ratio. Moreover, the. fact that the synchronizingsignals are transmitted at carrier frequencies means that there can beno interaction between these signals in my improved systemof'television, since no cross modulation effects can take place unlessthere be a simultaneous transmission of the two signals. Since thetransmission of the sound signals is restricted to the fiyback or returnline time, there can be no cross modulation or other interferencebetween the video and audio signals, since during the return line timethere is nov transmission of the video signals.

aBy frequency-modulating the shifted carrier for the line synchronizingsignals over a very wide band improved signal-to-noise ratio for thesound signal is obtained. As is well known in the art, thesignal-to-noise ratio in frequency modulation is improved as the ratioof the frequency shift tothe maximum rate of frequency shift is madegreater. Since I provide a ratio on the order of 200, thesignal-to-noise-ratio in the disclosed system is high so that aconsequential improvement in sound reproduction results.

Accordingly, it is the main objective of my invention to provide anewand improved method,

7 system, and apparatus for television transmission.

Another objective of my invention is to provide a televisiontransmitting system utilizing only a single transmitter and antenna.

A further objective of my invention is to provide a television systemrequiring only a single antenna and receiver 'for receiving both sightand sound signals.

Yet another objective of my invention is to provide method and apparatusfor transmitting from a single antenna amplitudeor frequency-modulatedsignals for pictures, frequency shifted carriers for line and framesynchronizing signals, and frequency modulated shifted carrier signalsfor the accompanying sound.

A still further objective of my invention is to provide a new method andapparatus for transmitting and receiving video and audio si nalsrequiring only a single transmitter and receiver and having improvedsignal-to-noise ratio for synchronizing and sound signals, greaterdefinition, and complete avoidance of cross modulation between sight andsound signals, and line and frame synchronizing signals.

Other objects of my invention will become evident upon reading thedetailed description of my invention taken together with the drawings.

In the drawings, Figure 1 is a graphical representation of televisionsignals interspersed with synchronizing signals. Figure 2 is a graphicalrepresentation of the utilization of the frequency spectrum comparedwith the antenna transmission characteristic. Figure 3 shows a blockeddiagram of a transmitter embodying my invention, while Figure 4 shows ablocked diagram of a receiver embodying the principles of my invention.

Turning now to Figure 1, there is shown the emitted signal of atransmitter incorporating my invention and amuming negative modulation,as understood in the art, in which the peak value I represents the linesynchronizing interval, during which time no video signals aretransmitted, while the portion 3 of the curve represents the videosignal. The interval during which the video or picture signals aretransmitted isshown by the. letter P, while the interval of thesynchronizing signal is shown by the letter S. The synchronizing signalamplitude extends from the black level 5 on the order of 75% of themaximum amplitude to the maximum amplitude shown on the scale as 100%.The audio signals are transmitted only during the retrace or flybackintervals s and are transmitted as frequency modulation of the linesynchronizing pulses. It will be appreciated that the frequency of theline synchronizing pulses has been, in accordance with my invention,shifted inofrequency from the frequency, Io, of the video signals to adifferent frequency,

f1. This is indicated in Figure 1 where the line synchronizing pulseshave a frequency. f1, while the frequency of the carrier for the videosignals is indicated as 10. At the end of each frame a framesynchronizing signal having a similar amplitude characteristic of thatof the line synchronizing signal, but a different frequency. ft, istransmitted.

The line and frame synchronizing pulses are preferably (although notnecessarily) of constant height, extend above the black level, 5, andare separated from the video signals by amplitudeselection at thereceiver. Since the line and frame synchronizing signals occupydifferent frequency ranges, frequency selection after the amplitudeselection will differentiate between the line and frame signals. Thefrequency selection serves also to exclude the frame signal impulsesfrom the discriminator circuit, which serves to extract the audiomodulation from the sound frequency modulated line synchronizingsignals. No loss in signal-to-noise ratio for the sound signal isexperienced, even though the sound signal is transmitted for only 10 to15% of the time because a very wide frequency swing is provided for thesound signals. Moreover, during the picture interval (-90%) in which nosound signal is received no noise can be received in the sound channelbecause the noise is suppressed together with the picture signals in theamplitude selector,

In Figure 2 there is shown a frequency spectrum in which the solid line9 represents the over- 1 all response of the vestigial sideband'transmitter and receiver for the video signals during the periods Pof a 525-line 30-frame system, for example. The broken line II shows theover-all response of the transmitter and receiver during the fiybacktime interval 8 for the line synchronizing pulses extending, forexample, from fo minus 1 megacycle to f0 plus 2 mc., while in is thecarrier frequency of the video modulation. This band of 3 mo. widthyields line synchronizing impulses, of a frequency of the order of 15kc. for the assumed system, of ample steepness and permits frequencymodulation of the sound signals over a frequency range of :1 mc. Theline synchronizing pulse is shifted during its transmission time to afrequency of {a plus 0.5 mc. The dotted line l3 represents the over-allresponse curve for the frame timing impulses in which the carrier isshifted to a different frequency 1: equal to, as shown in the diagram,for example, In plus 3 mo. A band width of *;0.5 mc. is provided toinsure ample steepness of the frame signal wave front. The frame,impulse may, for example, be sent out during the picture period havinga duration equal to that of the line synchronizing impulses, or even aslong as 25% of a line scanning period, and commencing 5% of a linescanning period after the end of the line synchronizing signal for evenfields, and 55% of a line scanning period after the end of a linesynchronizing signal for the odd fields in an interlaced picture system.

More specifically, my method may embody apparatus shown schematically inFigure 3. Since my method utilizes conventional apparatus such as iswell known in the art, a block diagram has been used in order tosimplify the complete understanding of the operation 'of my system. Waveenergy from a carrier oscillator 21 is amplified by a suitable amplifier35. The amplified carrier is then modulated in the modulator ll bysignals from the camera amplifier 31, which .is keyed by the retraceblanking unit 39. The retrace blanking unit is fed from the line pulsegenerator 3| so that during the time of transmission of the linesynchronizing impulses no signals are fed from the amplifier 31 to themodulator 4|. 7

to control both the line pulse generator 3| and the frame pulsegenerator 33. A portion of the frame pulse generator output is also fedto the retrace blanking unit 39 to prevent transmission of the picturesignal during the framing synchronizing interval. The retrace blankingunit and line and frame pulse generator may be of the type shown inSmith, U. S. Patent No. 2,- 132,655. A microphone amplifier 2| feeds theam-' plified sound signals to a frequency modulator 25 through a keyingtube 23. The keying tube 23 is actuated by the line pulse generator 3|to pass the audio signals from the amplifier 2| to the frequencymodulator; that is to say, normally the keying tube is in a blockedcondition so that no sound signals get through. The occurence of a linesynchronizing signal, however, unblocks the keying tube 23 and permitsthe sound signal to pass through the frequency modulator to frequencymodulate the carrier. The keying tube 23 may be of the formcorresponding to the keyed amplifier of the Zworykin U. S. Patent No.2,- 146,376. The line pulse generator 3| also passes signals directly tothe frequency modulator 25, and its amplitude is so chosen to shift thefrequency of the carrier to a value of f0 plus 0.5 me. The frame pulsegenerator 33 also feeds signals to the frequency modulator 25, which maybe of the type shown in Finch U. S. Patent 2,- 225,691, which signalshave an amplitude sufficient to shift the frequency of the carrier fromf0 to jo plus 3 mc. The carrier amplifier 35 serves both to amplify themodulated energy from the carrier oscillator 21 and to limit theamplitude of the carrier so as to suppress all spurious amplitudemodulation. Theoutput of the amplifier 35 is then fed to the amplitudemodulator 4|. The output of the modulator 4| is then fed, if a vestigialsideband system is used, to the vestigial side band filter 41. Theoutput of the filter 41 feeds through the synchronizing or timing pulsekeying unit 45 to the power stage of the transmitter 43 and is thenceradiated by the antenna 49 The timing pulse keying unit 45 is actuatedby signals from both the generator 3| and the generator 33 to increasethe carrier level from the black level 5 of Figure 1 to maximum level IIn Figure 4 there is shown a blocked diagram for a receiver embodyingprinciples of my invention and adapted to reproduce both picture andsound from the signals transmitted from the antenna 49, in which theunits may be of conventional design known in the art. In Figure 4 theantenna 5| receives the transmitted signals and the received signals,fed to a conventional television receiver, are amplified by the radiofrequency amplifier 53. The amplified signals are passed to a mixer 51where they are heterodyned by energy from the oscillator 55, detectedand passed to an intermediate frequency amplifier- 59. The intermediatefrequency amplifier may be of conventional design and passingfrequencies from in minus 1 me. to in plus 3 mc. with substantiallyconstant gain, dropping off slowly to it plus 5 mc. The output of theintermediate frequency amplifier 59 is then split up as follows:

A portion of the output is fed to the video rectifier 83 and thence to avideo amplifier 85 and to the control electrode of a cathode ray tube.

A master pulse generator 29 serves- The direct current component of therectifier output is fed to the AVG system 6| in conventional manner. TheAVC, in turn, serves to control the gain of the amplifiers 53 and 59.Another portion of the output of the amplifier 581s fed to an amplitudeseparator 63, known in the art as the zero bias detector type or of theconventional type in which an amplifiertube is biased beyond cut-off sothat it responds only to amplitudes extending above the black level,that is to say, to the frame and line synchronizing signals. This servesto suppress the picture signals in the output of the separator 63, andthe output containing the line andframe synchronizing signals is thenpassed through a pair of filters 65 and 1|. The filter 65 has amid-frequency of f0 plus 3 mc. and has a band width of $0.5 mc. Thisfilter, therefore,

permits only the frame signals to pass through,

which signals are then utilized to control a frame sweeposcillator 61,the output of which produces vertical deflection of the cathode ray beamof the kinesqope. The filter H has a mid-frequency of fo plus 0.5 mo.and a band width of :1.5. As a result, only the line synchronizingfrequency modulated pulses can pass through the filter ll. The'output ofthe filter, on one hand, is rectified and fed to the line sweeposcillator 13 to provide a synchronized horizontal deflection of thecathode ray beam.

A portion of the output ofthe filter H is also fed to a limiter H andthence to a frequency discriminator, of the kind shown in U. S. PatentNo. 2,229,640 to Crosby, and rectifier 19, which includes a low-passfilter having a cut-off frequency substantially equal to one-half theline synchronizing frequency. The output of the lowpass filter feeds theaudio amplifier 8|, which, in turn, feeds the loud speaker 82, toprovide a reproduced sound. It will be appreciated that the audioamplifier 8| may include a suitable integrating circuit, such as is wellknown in the art, for reproducing the sound. It will be furtherappreciated-that energy from the vertical and horizontal deflectioncircuits can be supplied to the cathode ray tube control 81 to providesuitable blanking out during return line time of the cathode ray tube.

It is helpful to remember that no two signals can interfere with eachother unless they'are simultaneous. Thus there can be no interactionduring the picture periods P (Figure 1), since during these the videomodulation alone is transmitted.

During the transmission of the synchronizing pulses, the video rectifierreceives signals of constant height and varying carrier frequency. Allthese pulses are rectified equally well, yieldin blacker-than-blackpulses suitable for blacking out the retrace of the beam. As statedabove, there is no trace of picture signals left in the anode circuit ofthe amplitude selector tube, only line and frame synchronizing pulses.Any interaction between them, such as cross modulation in the non-linearcut-off region of the amplitude "selector tube, is ruled out since thesepulses never These units may all be of conventional design.

occur at the same time; overlap of transient phenomena is excluded byample intervals between line and frame synchronizin pulses of at least0.05 of the horizontal scanning period.

The sideband frequencies of the frame synchronizing pulse are restrictedto about +0.5 me. and therefore cannot penetrate into the frequencyrange reserved for the linesynchronizing pulses. Yet this bandwidthpermits the frame synchronizing pulse to rise from 0.1 to 0.9 of itsfinal height in Just over .01 of the horizontal scanning period, thougha rise one-tenth as fast would suffice for accurate interlace.

The line timing or synchronizing pulses. during moments of silence, whenthe carrier is at In plus 0.5 mc., may occupy a band of 3 megacycleswidth. Thus the front of the rectified line timing pulses may rise from0.1 to 0.9 flnal height in about 0.30 microsecond. This steepness offront compares well with the present R. M. A. standard requiring thepulses to rise to their final level in 0.005 ofthe horizontal scanningperiod.

However, the carrier of the line timing pulse will seldombe at thecenter of the allotted band, swinging up to +0.5 megacycle with theaudio modulation. It may be suspected that the front of the pulses maydepend, in steepness and shape, on the momentary position of theswinging carrier in the band. Such an effect theoretically exists, butit is fortunately very small and experience shows that it may beneglected.

Change of the carrier frequency during the time of a pulse can beneglected, since the pulses are short compared with the period of thehighest sound frequency.

The effect of the line synchronizingpulse on the sound modulation, thatis, the fact that the sound tranlnitted only during discrete shortbursts of a frequency-modulated carrier, does not impair the quality ofsound reproduction. The pulses, limited to equal height, will produce inthe frequency discriminator circuit bursts of oscillations of a heightvarying in linear proportion to the modulated frequency. The output ofthe rectifier thus contains, apart from the i/ carrier frequency andsidebands, not only the envelope of these pulses of the soundmodulation, but also the pulses themselves. These pulses represent asubcarrier frequency amplitude-modulated by the audio modulation, but solong as the low-pass filter in the audio detector has a frequencycut-off substantially equal to one-half of the line frequency, therewill be no overlap between the audio band and the eflective lowersideband frequencies of the line synchronizing impulses.

It will be appreciated that while concrete examples of the magnitude ofthe frequency shift of the carrier and the bandwidths have been given,these. values were merely mentioned to make applicant's invention clear.It will'also be appreciated that where it is desired to achieve greatersteepness of the line synchronizing pulses that a wider bandwidth than 3me. may be provided with a corresponding suitable shift of the carrier.Moreover, it will be appreciated that in the event that the televisionchannel is broadened out that the over-all response curve shown inFigure 2 may. correspondingly be increased, that is to say, in general,the values are merely indicated for descriptive purposes and are not tobe construed as specific values which must be followed in order toderive the benefits of my invention.

It will be further appreciated that while a number of patents have beencited to show conventional embodiments, these citations were merely byway of example and that it is not necessary to utilize the specificembodiments disclosed by these patentees. The citations were made by wayof example and, of course, any other forms of conventional apparatusknown in the art may be substituted or utilized without departing fromthe scope of my invention.

Various alterations and modification of the present invention may becomeapparent to those skilled in the art and it is desirable that any andall such modifications and alterations be considered within the purviewof the present invention except as limited by the hereinafter appendedclaims.

Having described my invention, what I claim is:

1. The method of reproducing images and sound accompaniments whichincludes the steps of producing video signals representative of theimage to be reproduced, generating carrier oscillations of apredetermined frequency, modulating the produced carrier oscillations bysaid video signals, generating line synchronizing pulses and framesynchronizing pulses, generating signal energy representative of thesound accompanying the video signals, interrupting the video signalmodulation of the carrier frequency under the control of the linesynchronizing pulses, producing a shift in the frequency of thegenerated carrier to a differentvalue during the intervalsofinterruption of video signal modulation, frequency-modulating theshifted frequency carrier "by the sound signal energy, periodicallyshifting the predetermined frequency to a second different value underthe control of the frame synchronizing signals, transmitting all of saidmodulated and frequency shifted carrier frequency oscillations,receiving the transmitted carriers, demodulating the received carriers,segregating the video signals from the line synchronizing, framesynchronizing, and audio signals, segregating the line synchronozingsignals from the frame synchronizing signals, frequency-demodulating thelimited signals, producing sound under the control of the frequencydemodulated signals, and synthesizing the image under the control of thesegregated video signals and both the line synchronizing and framesynchronizing pulses.

2. The method of transmitting signals representative of images and soundaccompaniments which includes the steps of producing video sigi nalsrepresentative of the image to be reproduced, generating carrieroscillations of a predetermined frequency, modulating the producedcarrier oscillations by said video signals, generating linesynchronizing pulses and frame synchronizing pulses, generating signalenergy representative of the sound accompanying the video signals,interrupting the video signal modulation of the carrier; frequency underthe control of the line synchronizing pulses, producing'a shift in thefrequency of the generated carrier to a different value during theintervals of interruption of video signal modulation,frequency-modulating the shifted frequency carrier by the sound signalenergy, periodically shifting the predetermined frequency to a seconddifferent value under the control of the frame synchronizing signals,and transmitting all of said modulated and frequency shifted carrierfrequency oscillations.

3. The method of reproducing images and sound accompaniments whichincludes the steps of producing video signals representative of theimage to be reproduced, generating carrier oscillati ons of apredetermined frequency, amplitudemodulating the produced carrieroscillations by said video signals, generating line synchronizing pulsesand frame synchronizing pulses, generating signal energy representativeof the sound accompanying the video signals, interrupting the video 7.6signal modulation of the carrier frequency under the control of theframe synchronizing signals,

the control of the line synchronizing pulses, shifting the generatedcarrier frequency to a different value during the intervals ofinterruption of video signal modulation, frequency-modulating theshifted frequency carrier by the sound signal energy, periodicallyshifting the predetermined frequency to a second different value underthe control of the frame synchronizing signals, transmitting all of saidmodulated and frequency shifted carrier frequency oscillations,receiving the transmitted carriers, demodulating the received carriers,segregating the video signals from the line synchronizing, framesynchronizing, and audio signals, segregating the line synchronizingsignals from the frame synchronizing signals, limiting the separatedline synchronizing signals, frequency-demodulating the limited signals,producing sound under the control of the frequency demodulated signals,and synthesizing the image field under the control of the segregatedvideo signals and both the line synchronizing and frame synchronizingpulses.

4. The method of reproducing images and sound accompaniments whichincludes the steps of producing video signals representative of theimage to be reproduced, generating carrier oscillations of apredetermined frequency, frequencymodulating the produced carrieroscillations by said video signals, generating line synchronizing pulsesand frame synchronizing pulses, generating signal energy representativebf the sound accompanying the video signals, interrupting the videosignal modulation of the carrier frequency under the control of the linesynchronizing pulses, controlling the carrier frequency generation toproduce a carrier frequency of a difierent frequency value during theintervals of interruption of video signal modulation,frequency-modulating the shifted frequency carrier by the sound signalenergy, periodically shifting the predetermined frequency to a seconddifferent value under the control of the frame synchronizing signals,transmitting all of said modulated and frequency shifted carrierfrequency oscillations, receiving the transmitted carriers, demodulatingthe received carriers, segregating the video signals from the linesynchronizing, frame synchronizing, and audio signals, segregating theline synchronizing signals from the frame synchronizing signals,limiting the separated linesynchronizing signals, frequency-demodulatingthe limited Sig-- nals, producing sound under the control of thefrequency demodulated signals, and synthesizing the image field underthe control of the segregated video signals and both the linesynchronizing and frame synchronizing pulses.

5.' The method of reproducing images and sound accompaniments whichincludes the steps of producing video signals representative of theimage to be reproduced, generating carrier oscillations of apredetermined frequency, modulating the produced carrier oscillations bysaid video signals, generating line synchronizing pulses and framesynchronizing pulses, generating signal energy representative of thesound accompanying the video signals, interrupting the video signalmodulation of the carrier frequency under the control of the linesynchronizing pulses, controlling the generation of the carrierfrequency oscil-- lations to produce an output .of a different frequencyvalue during the intervals of interruption of video signal modulation,frequency-modulating the shifted frequency carrier by the sound signalenergy, periodically shifting the predetermined frequency to a seconddifierent value under transmitting all of said modulated and frequencyshifted carrier frequency oscillations, receiving the transmittedcarriers, demodulating the received carriers, segregating the videosignals from the line synchronizing, frame synchronizing, and

audio signals, detecting the segregated video 513- nals, segregating theline synchronizing signals from the frame synchronizing signals,limiting the separated line synchronizing signals,frequency-demodulating the limited signals, producing sound under thecontrol of the frequency demodulated signals, and synthesizing the imagefield under the control of the detected video signals and both the linesynchronizing and frame synchronizing pulses.

6. A television transmitting system comprising a television camera, amaster pulse generator for controlling the scanning of said camera, aline pulse generator, a frame pulse generator, means to control saidline pulse and said frame pulse generators from said master pulsegenerator, a carrier wave oscillator, an amplitude modulator forcontrolling the amplitude of the energy from said carrier waveoscillator, means to actuate the said modulator by energy resulting fromthe scanning of said camera, means to periodically interrupt saidactuation by the line pulse and frame pulse generators, means totransmit the amplitude modulated carrier wave energy, a source of soundenergy, a frequency modulator, means to energize the frequencymodulatorby said source of sound energy, means to connect the frequency modulatorto the carrier wave oscillator to vary the frequency thereof, means tointerrupt the 'energization ofthe frequency modulator by the said linepulse and frame pulse and amplitude modulated by said signals from thecamera,

'7. A television system comprising a television camera, a master pulsegenerator for controlling the scanning of said camera, a line pulsegen-.

erator, a frame pulse generator, means to control said line pulse andsaid frame pulse generators from said master pulse generator, a carrierwave oscillator, an amplitude modulator for controlling the amplitude ofthe energy from said carrier wave oscillator, means to actuate the saidmodulator by energy resulting from the scanning of said camera, means toperiodically interrupt said actuation by the line pulse and frame pulsegenerators, means to transmit the amplitude modulated carrier waveenergy, a source of sound energy, a frequency modulator, means to ener-'gize the frequency modulator by said source of soundenergy, means toconnect the frequency modulator to the carrier wave oscillator to varythe frequency thereof, means to interrupt the energization of thefrequency modulator by the said line pulse and frame pulse generatorsduring the time interval in which the amplitude modulator is actuated,means to shiftthe frequency receive the transmitted energyrepresentative of the synchronizing sight and sound signals, means todetect the received signals, amplitude separator means to segregate theline and frame synchronizing pulses from the camera signals, filtermeans to separate the line synchronizing pulses from the framesynchronizing pulses, means to control vertical deflection oi a cathoderay tube by the separated frame synchronizing pulses,

means to control the horizontal deflection of said 10

